The present invention relates to a cooling system for a rotating electrical machine and, more particularly, to a modified cooling circuit in a reverse flow electric power generator incorporating a contoured seal ring surface.
When cooling fans are mounted at the ends of rotating electrical machines, such as large power generators, they produce high pressure cooling air for distribution to the interior portions of the machine that need to be cooled. In cooling configurations, such as the prior art configuration shown in FIG. 1 xe2x80x94sometimes known as a xe2x80x9creverse flow cooling system,xe2x80x9d the cooling fan exhausts hot gas from the interior of the machine that has been cooled and directs this hot gas either to a heat exchanger to be cooled before re-entering the machine or exhausts it from the machine. In close proximity to this high pressure hot fan discharge is the inlet to the rotor, where lower pressure cold cooling gas is drawn by pumping suction into the rotor to cool it. A seal must be positioned between the high pressure hot gas discharging from the fan and the low pressure cold gas inlet to the rotor, or the rotor will detrimentally ingest hot gas into its cooling stream.
Typically, a clearance seal is positioned between the hot fan outlet and the cold rotor inlet to separate the two flow streams. A clearance seal relies on finely controlled clearance spaces between the rotating body and the non-rotating seal to inhibit the flow of hot gas into the rotor inlet. This construction, however, poses some problems. First, the fine clearances must be accurately and tightly controlled to provide minimal leakage of hot gas, which results in a difficult and costly assembly of rotating and stationary components. Second, since the fan discharges at a high pressure and the rotor inlet is at a lower pressure, some hot gas will inherently be drawn into the cold rotor inlet by virtue of the necessary finite clearance of the seal, resulting in ineffective rotor cooling and efficiency losses due to the recirculation of leaking hot gas.
While positive contact seals could be used to provide sealing between rotating and stationary parts, these contacting seals increase costs and produce a high amount of rotating drag friction that decreases the overall efficiency of a rotating machine. Non-contacting seals provide higher efficiency at lower costs and complexity.
In an exemplary embodiment of the invention, a cooling system for a rotating electrical machine includes a cooling fan that serves to exhaust hot gas from an interior of the machine, a seal ring surface defining a passage for the exhausted hot gas, and a clearance seal positioned in the passage between the rotating body of the machine and a non-rotating body of the machine to prevent the exhausted hot gas from entering an inlet to the rotating body. The seal ring surface is shaped to impart sufficient momentum to the exhausted hot gas to prevent the exhausted hot gas from leaking into the rotating body inlet. The seal ring surface may be shaped such that the passage is narrower toward the rotating body inlet and wider away from the rotating body inlet. The passage preferably extends from the clearance seal to a diffuser, wherein the seal ring surface is contoured to direct the exhausted hot gas toward the diffuser. In one preferred construction, the rotating electrical machine is a power generator, the rotating body is a generator rotor, and the non-rotating body is a generator stator.
In another exemplary embodiment of the invention, a reverse flow electric power generator cooling circuit includes a cooling fan exhausting hot as from an interior flow passage between the rotor and the stator to an exhaust passage. A diffuser at one end of the exhaust passage receives the exhausted hot gas, and a rotor inlet passage is provided at an opposite end of the exhaust passage. A clearance seal is disposed between the interior flow passage and the rotor inlet passage to prevent the exhausted hot gas from entering the rotor inlet passage. The exhaust passage is shaped to impart momentum to the exhausted hot gas away from the rotor inlet passage.